Ecological Disturbance Regimes Research Articles

A flexible data‐driven approach to co‐producing drought vulnerability assessments

AbstractIntensifying weather events are key characteristics of climate change that are fundamentally changing ecological disturbance regimes. Intensifying drought is a particular threat to species, ecosystems, and ecosystem services worldwide. Proactive drought adaptation measures are acutely needed, but without a better understanding of drought vulnerability at the appropriate scale and geography, such measures may not be effective, or even anticipated as potential options. A recent conceptual framework for ecological drought aligns a holistic suite of potential drivers with the key components of climate change vulnerability (exposure, sensitivity, and adaptive capacity). We leverage the ecological drought framework and components of vulnerability to introduce a six‐step process for developing a drought vulnerability assessment (DVA) that (1) is place‐based and avoids mismatches between assessment geography and management action, (2) uses existing empirical datasets and leverages machine learning techniques and remotely sensed data from a recent drought, (3) emphasizes the inclusion of stakeholders and the importance of data visualization and science communication, and (4) is flexible and adaptable to a wide range of planning contexts. We illustrate the DVA process with a case study for forested watersheds in the Missouri Headwaters (MH), Montana, USA, that is focused on the impact of an early 2000s drought event on forest health. We show how the DVA provides insights on drought vulnerability that are helpful starting points for co‐developing region‐specific management actions to prepare for the next drought, including strategies to enhance ecologically available water, reduce competition for water, promote ecosystem persistence under drought conditions, and prioritize sites for forest restoration, transition, or protection. The work described here provides a model for developing a DVA in other places that, when used in a participatory adaptation planning process, supports the implementation of effective adaptation strategies.

Military activity and wetland-dependent wildlife: A warfare ecology perspective.

Wetlands provide unique habitat functions that benefit society by provisioning food, recreation, and ecosystem sustainability. Warfare affects the habitats of wetland-dependent reptiles, amphibians, and birds in both positive and negative ways, and opportunities exist to improve the management of wildlife habitat using a warfare ecology framework. Recent events in Ukraine highlight these relationships and provide stimulus to further consider the implications of current events for natural resources. In response, this commentary highlights both degradational and positive impacts of warfare on wetland fauna during the cyclical preparation, active conflict, and recovery phases. For example, the active conflict phase often initiates ecological disturbance regimes that couple large-scale landscape alteration with the release of chemicals and other materials into wetlands, leading to reduced reproductive potential and population declines in wetland-dependent species (e.g., amphibians, waterfowl) along with decreased overall wetland biodiversity and habitat quality. In contrast, wetland-dependent wildlife can benefit from (1) conservation activities occurring on military installations maintained to support training activities and (2) restoration efforts initiated after the cessation of combat. For example, many threatened and endangered reptiles and amphibians find refugia on military lands in the USA and internationally, and international protections for wetland resources (including the Ramsar Convention) have been established to promote their sustainability and wise use. Additional research is needed to improve the protection of valuable wetland resources by further enhancing ongoing conservation and planning efforts and improving strategies to mitigate the negative impacts of warfare on wetland dependent species throughout each phase of the warfare ecology cycle. Integr Environ Assess Manag 2024;20:2153-2161. Published 2023. This article is a US Government work and is in the public domain in the USA. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Assessing genetic structure of Eugenia uniflora L. populations along an environmental gradient using a novel set of SSR markers

Gradients in biodiversity are often considered a result of environmental variables like temperature, precipitation, ecological disturbance regimes, and species coexistence. This study aimed at investigating the genetic diversity and structure of natural populations of Eugenia uniflora growing in two different biomes in southern Brazil (Atlantic Forest and Pampa biomes), as well as in the transition zone between them. A novel set of 11 SSR loci from E. uniflora was validated and employed to test the hypothesis that the allelic composition of the populations changes gradually along the environmental gradient sampled, with a characteristic genetic structure within each biome and an intermediary allelic composition in the transition zone. The results revealed high polymorphism of the validated markers and significant genetic structure of the different populations. The main source of genetic variation observed is the individual samples, but there was a considerable amount of variation among populations, and regions. We suggested that the genetic structure of the studied populations presents distinct patterns which may be related to adaptation to local environmental conditions, or at least related to the transition among them. Our study provides evidence that even environments neglected regarding the information on their biodiversity and the transition zones may hold important levels of genetic diversity. Thus, the distribution of genetic diversity should be interpreted in the light of the life traits of the species and the local environment since valuable diversity may be found both in a hotspot of diversity and in neglected forest formations.

A palaeovegetation and diatom record of tropical montane forest fire, vegetation and hydroseral changes on Mount Kenya from 27,000–16,500 cal yr BP

Fire is an important ecological disturbance in moist tropical forests influencing vegetation composition and structure. Contemporary and historical records of forest fires in mountain forests of Kenya are limited to the past decades and have a strong anthropogenic influence for ignition patterns and fire suppression activities. Palaeoenvironmental geoarchives provide the temporal depth to investigate long-term (multidecadal-to-millennial) changes in fire activity. Here we use a sediment record from the Rumuiku wetland, located in a volcanic crater on the eastern flank of Mount Kenya that was radiocarbon dated and analysed for diatom, pollen and charcoal subfossils to produce a highly resolved time series of local hydroclimatic change, vegetation, and fire; respectively. This study focuses on the time during and following the global Last Glacial Maximum, a time of rapid warming and changing regional hydroclimate with relatively stable atmospheric CO2 and not yet intensive anthropogenic modification of ecosystems. Charcoal and pollen data support associated changes in vegetation-fire centred around 21,500 cal yr BP when Afromontane forests with predominant abundances of Juniperus, Podocarpus and other montane forest trees changed to Hagenia-dominated forests that are relatively more open and adapted to burn more frequently but with less intense fires.These transitions in ecosystem composition, distribution and structure support the important role of fire in driving and maintaining forest composition in the watershed and contributing to the spatial complexity of forests around the mountain. These changes in composition, structure and biomass occurred during a time of rapid Late Pleistocene climate warming, regional hydroclimatic drying, and slowly rising atmospheric CO2 from 27,000 to 16,500 cal yr BP, during and following the conditions of the global Last Glacial Maximum. Temperature, hydroclimate and atmospheric CO2 are well-known drivers of montane vegetation change in the tropics and the role of fire is shown here to be a contributing driver to the spatial heterogeneity of forest patches at long time scales. Vegetation modelling at spatial scales relevant to land management and conservation should include retrospective evidence of the range of drivers of ecological disturbance regimes.

The species diversity × fire severity relationship is hump‐shaped in semiarid yellow pine and mixed conifer forests

AbstractThe combination of direct human influences and the effects of climate change are resulting in altered ecological disturbance regimes, and this is especially the case for wildfires. Many regions that historically experienced low–moderate severity fire regimes are seeing increased area burned at high severity as a result of interactions between high fuel loads and climate warming with a number of negative ecological effects. While ecosystem impacts of altered fire regimes have been examined in the literature, little is known of the effects of changing fire regimes on forest understory plant diversity even though understory taxa comprise the vast majority of forest plant species and play vital roles in overall ecosystem function. We examined understory plant diversity across gradients of wildfire severity in eight large wildfires in yellow pine and mixed conifer temperate forests of the Sierra Nevada, California, USA. We found a generally unimodal hump‐shaped relationship between local (alpha) plant diversity and fire severity. High‐severity burning resulted in lower local diversity as well as some homogenization of the flora at the regional scale. Fire severity class, post‐fire litter cover, and annual precipitation were the best predictors of understory species diversity. Our research suggests that increases in fire severity in systems historically characterized by low and moderate severity fire may lead to plant diversity losses. These findings indicate that global patterns of increasing fire size and severity may have important implications for biodiversity.

Scaling and Complexity in Landscape Ecology

Landscapes and the ecological processes they support are inherently complex systems, in that they have large numbers of heterogeneous interacting components, interact in multiple ways, and exhibit scale dependence, non-linear dynamics, and emergent properties. The emergent properties of landscapes encompass a broad range of processes that influence biodiversity, ecosystem processes, and human environments. These properties, such as nutrient cycling, dispersal, evolutionary adaptation of organisms to their environments, and the focus of this article, ecological disturbance regimes (including wildfire), operate at scales that are relevant to human societies, but these are also often the scales at which ecosystem dynamics are most difficult to understand and predict. Modeling processes and interactions at the landscape scale, including future states of biological communities and their interactions with each other and with processes such as landscape fire, requires quantitative metrics and algorithms that minimize error propagation across scales. We identify three intrinsic limitations to progress in landscape ecology, and ecology in general: (1) the problem of coarse-graining, or how to aggregate fine-scale information to larger scales in a statistically unbiased manner; (2) the middle-number problem, which describes systems with elements that are too few and too varied to be amenable to global averaging, but too numerous and varied to be computationally tractable; and (3) non-stationarity, in modeled relationships or parameter choices that are valid in one environment but may not hold when projected onto future environments such as a warming climate. We illustrate these challenges with examples drawn from the context of landscape ecology and wildfire. Quantitative scaling relationships are the key to moving forward, and we review recent progress and paths to developing scaling laws in landscape ecology. We incorporate concepts of compression of state spaces from complexity theory to suggest ways to overcome the problems presented by coarse-graining, the middle-number domain, and non-stationarity.

Fire Regime Alteration in Natural Areas Underscores the Need to Restore a Key Ecological Process

Research Natural Areas (RNAs) are federal lands designated to protect exemplary, relatively undisturbed ecosystems where ecological processes may proceed unencumbered with minimal human intervention. Ideally, RNAs serve as properly functioning reference sites for more heavily managed landscapes. However, many RNAs have been modified to some degree by past and ongoing human actions. In the western United States, these actions commonly result in altered disturbance regimes, most notably fire. Ecological disturbance regimes are important components of natural ecosystems, and major changes to such regimes challenge the usefulness of the RNA system as a reference network. To assess the extent of modern departure from their pre-Euroamerican settlement (i.e., pre-1850) fire regimes, we examined 64 RNAs on Forest Service lands in California. We found that 76% exhibited moderate to high fire regime departure. Of these, 87% are burning much less frequently than they would have under the presettlement fire regime and 13% are burning more frequently. Within RNAs, ecosystems historically characterized by frequent, mostly low-severity fire have missed multiple fire cycles and tend to burn at higher fire severities than expected under the presettlement fire regime. We present four case studies that demonstrate how recent wildfires have affected California RNAs. We also indicate where and how future fire management strategies could address altered fire regimes and more effectively sustain target ecosystems within RNAs. Our findings suggest that a re-examination of the hands-off approach to management in some protected natural areas like RNAs is needed.

Ecological Response to Permafrost Thaw and Consequences for Local and Global Ecosystem Services

The Arctic may seem remote, but the unprecedented environmental changes occurring there have important consequences for global society. Of all Arctic system components, changes in permafrost (perennially frozen ground) are one of the least documented. Permafrost is degrading as a result of climate warming, and evidence is mounting that changing permafrost will have significant impacts within and outside the region. This review asks: What are key structural and functional properties of ecosystems that interact with changing permafrost, and how do these ecosystem changes affect local and global society? Here, we look beyond the classic definition of permafrost to include a broadened focus on the composition of frozen ground, including the ice and the soil organic carbon content, and how it is changing. This ecological perspective of permafrost serves to identify areas of both vulnerability and resilience as climate, ecological disturbance regimes, and the human footprint all continue to change in this sensitive and critical region of Earth.

In ecoregions across western USA streamflow increases during post-wildfire recovery

Continued growth of the human population on Earth will increase pressure on already stressed terrestrial water resources required for drinking water, agriculture, and industry. This stress demands improved understanding of critical controls on water resource availability, particularly in water-limited regions. Mechanistic predictions of future water resource availability are needed because non-stationary conditions exist in the form of changing climatic conditions, land management paradigms, and ecological disturbance regimes. While historically ecological disturbances have been small and could be neglected relative to climatic effects, evidence is accumulating that ecological disturbances, particularly wildfire, can increase regional water availability. However, wildfire hydrologic impacts are typically estimated locally and at small spatial scales, via disparate measurement methods and analysis techniques, and outside the context of climate change projections. Consequently, the relative importance of climate change driven versus wildfire driven impacts on streamflow remains unknown across the western USA. Here we show that considering wildfire in modeling streamflow significantly improves model predictions. Mixed effects modeling attributed 2%−14% of long-term annual streamflow to wildfire effects. The importance of this wildfire-linked streamflow relative to predicted climate change-induced streamflow reductions ranged from 20%−370% of the streamflow decrease predicted to occur by 2050. The rate of post-wildfire vegetation recovery and the proportion of watershed area burned controlled the wildfire effect. Our results demonstrate that in large areas of the western USA affected by wildfire, regional predictions of future water availability are subject to greater structural uncertainty than previously thought. These results suggest that future streamflows may be underestimated in areas affected by increased prevalence of hydrologically relevant ecological disturbances such as wildfire.

Converting quadratic entropy to diversity: Both animals and alleles are diverse, but some are more diverse than others.

The use of diversity metrics has a long history in population ecology, while population genetic work has been dominated by variance-derived metrics instead, a technical gap that has slowed cross-communication between the fields. Interestingly, Rao’s Quadratic Entropy (RQE), comparing elements for ‘degrees of divergence’, was originally developed for population ecology, but has recently been deployed for evolutionary studies. We here translate RQE into a continuous diversity analogue, and then construct a multiply nested diversity partition for alleles, individuals, populations, and species, each component of which exhibits the behavior of proper diversity metrics, and then translate these components into [0,1]—scaled form. We also deploy non-parametric statistical tests of the among-stratum components and novel tests of the homogeneity of within-stratum diversity components at any hierarchical level. We then illustrate this new analysis with eight nSSR loci and a pair of close Australian marsupial (Antechinus) congeners, using both ‘different is different’ and ‘degree of difference’ distance metrics. The total diversity in the collection is larger than that within either species, but most of the within-species diversity is resident within single populations. The combined A. agilis collection exhibits more diversity than does the combined A. stuartii collection, possibly attributable to localized differences in either local ecological disturbance regimes or differential levels of population isolation. Beyond exhibiting different allelic compositions, the two congeners are becoming more divergent for the arrays of allele sizes they possess.

Agricultural land-use diversity and forest regeneration potential in human- modified tropical landscapes

A major challenge in tropical human-modified landscapes (HMLs) is meeting the ever-growing demand for agricultural products while conserving biodiversity and ecosystem services provided by forest ecosystems. Within this challenge, a major issue is the understanding of the forest potential to naturally regenerate in abandoned agricultural fields. To assess such potential, it is necessary to know the diversity of agricultural land uses in the landscape, quantify the ecological disturbance inflicted by such uses, and evaluate forest regeneration as a function of disturbance both at the field and landscape levels. Our previous work has shown that in abandoned fields the abundance and species diversity of regenerating rain forest trees decline as disturbance level increases. Here we aimed to achieve the following: 1) to quantify the diversity of agricultural land uses in HMLs; 2) to assess ecological disturbance regimes caused by different agricultural land uses, at the field and landscape scales; and 3) to identify groups of agricultural land uses with contrasting effects for forest regeneration at the landscape level. We approach these issues by using a case study of HMLs in a southeastern region of Mexico, which are representative of landscapes in the agricultural frontier in the Neotropics. We interviewed 68 landowners to gather information on agricultural land uses and management of 156 fields. Based on this information, we quantified an ecological disturbance regime associated with each field considering the following: field size (in hectares), duration of agricultural use (in years), and land-use disturbance severity (i.e. frequency or magnitude of fire, agrochemicals, machinery, grazing or removal of tree cover). By integrating disturbance inflicted by different land uses and the proportion of the landscape covered by each land use, we constructed a landscape ecological disturbance index. Finally, by using this index and data gathered from nine landscapes (3×3km each), we tested the hypothesis that structural attributes (abundance, biomass, and species diversity of trees) of regenerating forests decrease as agriculture disturbances increase in the landscape. There was a high inequality in the proportion of land allocated to the 13 recorded agricultural land uses, with cattle pastures representing ca. 90% of total agricultural land. There was a wide disturbance gradient, ranging from land uses with high (e.g. cattle pastures) to low disturbance (e.g. coffee and cocoa plantations). Three major groups of land uses with contrasting disturbance regimes were detected: 1) agroforestry systems, characterized by small size, low to intermediate duration, and low disturbance severity; 2) monocultures, typically small size, long duration, and medium to high disturbance severity; and 3) extensive farming, large size, short to intermediate duration, and high disturbance severity. Biomass and species diversity of regenerating forests consistently reduced with increasing levels of agriculture disturbance in the landscape. We conclude that positive balances between biodiversity conservation and agricultural production in HMLs will depend on establishing agricultural land uses that inflict low disturbance regimes (such as agroforestry systems) embedded in a matrix of old-growth forest and long-lasting second-growth forests. Our results may inform farmers, policy makers and land managers about HMLs where agricultural production and conservation of biodiversity and ecosystem services can be conciliated.

Ecological disturbance regimes caused by agricultural land uses and their effects on tropical forest regeneration

AbstractAimsAcross tropical regions, large forest areas have been converted to different agricultural land uses. These uses impose ecological disturbances affecting forest regeneration potential after field abandonment. Finding ways to identify those agricultural land uses limiting forest regeneration is a critical issue for conserving biodiversity in human‐modified landscapes. Here, we developed a fast and inexpensive index, useful for quantifying ecological disturbance regimes associated with agricultural land uses, and tested its power to predict forest regeneration potential.LocationMunicipality of Marqués de Comillas, southeast Mexico.MethodsInterviews were conducted with local farmers to quantify disturbance components (size, duration and severity) associated with agricultural land uses. The scaled values of these disturbance components were added in a simple ecological disturbance index (EDI). In each one of nine recently abandoned fields representing a wide range of EDI values, two 10‐m2 plots, one close to and one far from nearby forest remnants, were established. On each plot, all woody plants of 10–100 m in height were counted, identified and measured in four 1‐m2 subplots, at the time of field abandonment and 2 yr later. In addition, at each plot, 18 site condition (microclimate and soil) attributes were quantified at the time of abandonment. Plant density, biomass, species richness and species diversity were used as regeneration variables, and EDI and site condition attributes as independent ones.ResultsTwo years after abandonment, most regeneration variables declined exponentially with EDI. Biomass was not explained by EDI but changed positively with light availability. EDI was strongly correlated to vapour pressure deficit, which also predicted regeneration potential (except biomass).ConclusionsEDI is a cheap and easy tool for quantifying the ecological disturbance produced by a wide range of agricultural land uses. The index predicted several regeneration variables as well as or better than direct measurements of the site condition at the time of abandonment. EDI can be used to identify biodiversity‐friendly agricultural land uses in human‐modified landscapes.

Historic livelihoods and land uses as ecological disturbances and their role in enhancing biodiversity: An example from Bhutan

International conservation efforts have ignored the role and importance of historic disturbance regimes, both natural and anthropogenic, in creating and maintaining biodiversity. In this article we focus on historic livelihoods and land uses which we argue can and should be viewed as a type of intermediate ecological disturbance that may increase landscape heterogeneity which is correlated with biological diversity. Using historic swidden in Bhutan as an example, we illustrate how this historic livelihood and land use maintained intermediate ecological disturbances in an otherwise densely forested landscape and increased plant structural heterogeneity, the proportion of early successional plant species, and the availability of forage and browse of importance to wild ungulates and their predators (e.g., tigers). The cessation of swidden in Bhutan and elsewhere alters historic disturbance regimes with potentially profound effects on flora and fauna. We argue that biodiversity conservation requires understanding and building upon ecological disturbance regimes which should include historic livelihoods and land uses. To be realized in practice, this requires not only further ecological study, but addressing the politics of knowledge.

Modern departures in fire severity and area vary by forest type, Sierra Nevada and southern Cascades, California, USA

Acute changes in ecological disturbance regimes can have major consequences for ecosystems and biota, including humans, living within them. Human suppression of fire in the western United States over the last century has caused notable changes to many ecosystems, especially in lower elevation, semiarid forest types dominated historically by fire tolerant taxa likePinusandQuercus. Recent increases in fire activity in western US forests have highlighted the need for restoration of ecological structure and function, but management targets for restoration in different forest types remain uncertain. Working in the forests of eastern California, we evaluated the direction and magnitude of change in burned area and fire severity between the period prior to Euro‐American settlement (∼1500–1850) and the “modern” period (1984–2009). We compared total annual area burned; proportional area burned at low‐moderate severity and high severity; and annual area burned at low‐moderate severity and high severity between the two time periods in seven forest types. We also examined modern trends in fire area and severity. We found that modern rates of burning are far below presettlement levels for all forest types. However, there were major differences between low to middle elevation forests and high elevation forests regarding the components of this departure. Low and middle elevation forests are currently burning at much higher severities than during the presettlement period, and the departure in fire area is overwhelmingly expressed in the low to moderate severity categories; in these forest types, mean annual area of high severity fire is not notably different between the modern and presettlement periods. In higher elevation forests on the other hand, the modern departure in fire area is expressed equally across fire severity categories. Our results underline the critical need for forest and fire restoration in the study area, especially in low and middle elevation forests adapted to frequent, low severity fire. Expanded management of naturally ignited fires for resource benefit is clearly needed, but in many parts of our study area, strategic reduction of forest fuels will likely be necessary before large‐scale restoration of fire becomes ecologically, politically, and financially feasible.

Fire effects on the spatial patterning of soil properties in sagebrush steppe, USA: a meta-analysis

Understanding effects of changes in ecological disturbance regimes on soil properties, and capacity of soil properties to resist disturbance, is important for assessing ecological condition. In this meta-analysis, we examined the resilience of surface soil properties and their spatial patterning to disturbance by fire in sagebrush steppe of North America – a biome currently experiencing increases in wildfire due to climate change. We reviewed 39 studies that reported on soil properties for sagebrush steppe with distinct microsite (undershrub and interspace) patterning that was or was not recently burned. We estimated microsite effects for 21 soil properties and examined the effect of burning on microsite effects during the first year post-fire, before the re-establishment of vegetation. Results indicated that the spatial patterning of biogeochemical resources, in which soil surfaces beneath shrubs are enriched, is resilient to burning. However, microsite effects for soil-surface hydrologic, temperature and erosion characteristics appeared to shift following burning. These shifts appear to create a negative feedback for the spatial patterning of soil properties before vegetation recovery. Relatively long (decades–centuries) historic fire intervals in sagebrush steppe ecosystems likely reinforce spatial patterning of soil resources. However, increased fire frequency might affect the ability for soil resources to withstand change.

1200 years of regular outbreaks in alpine insects

The long-term history of Zeiraphera diniana Gn. (the larch budmoth, LBM) outbreaks was reconstructed from tree rings of host subalpine larch in the European Alps. This record was derived from 47513 maximum latewood density measurements, and highlights the impact of contemporary climate change on ecological disturbance regimes. With over 1000 generations represented, this is the longest annually resolved record of herbivore population dynamics, and our analysis demonstrates that remarkably regular LBM fluctuations persisted over the past 1173 years with population peaks averaging every 9.3 years. These regular abundance oscillations recurred until 1981, with the absence of peak events during recent decades. Comparison with an annually resolved, millennium-long temperature reconstruction representative for the European Alps (r=0.72, correlation with instrumental data) demonstrates that regular insect population cycles continued despite major climatic changes related to warming during medieval times and cooling during the Little Ice Age. The late twentieth century absence of LBM outbreaks, however, corresponds to a period of regional warmth that is exceptional with respect to the last 1000+ years, suggesting vulnerability of an otherwise stable ecological system in a warming environment.